Hydraulic dampers, in particular a motor vehicle hydraulic suspension dampers, are known in the art. In a typical design the hydraulic damper comprises a tube filled with a working liquid, a main piston assembly disposed slidably inside a main section of the tube, with the main piston attached to a piston rod led outside the damper. The main piston divides the tube into a rebound chamber and a compression chamber, and is provided with both a rebound valve assembly and a compression valve assembly to control a flow of the working liquid within the tube during a rebound stroke and a compression stroke of the damper. In some designs having enhanced damping properties at least one end of the tube is provided with a narrowed section of a smaller diameter than the main section of the tube and the damper is further provided with at least one additional piston assembly, displaceable along with the main piston assembly and adapted to be slidably introduced into the narrowed section of the tube to generate additional damping force.
The additional piston assembly along with the narrowed section of the main tube forms what is called in the industry a hydraulic stop arrangement that generates additional damping force over a predefined end section of an operating travel range of the piston rod.
Exemplary dampers provided with such hydraulic stop arrangements are disclosed in patent publications EP 2 302 252 and EP 2 952 775. These hydraulic stop arrangements permit progressive generation of additional damping force depending not only on the additional piston assembly position but also on its velocity within the narrowed section, which may be tunable.
It is desirable to provide a hydraulic damper with a hydraulic stop arrangement that provides a progressive increase of damping force that is dependent on piston rod displacement but that also limits damping forces exceeding predefined and tunable thresholds. It is also desirable that such a damper should be of a simple construction, cost efficient and simple to manufacture and that the hydraulic stop arrangement might be applied as an add-on in existing damper constructions.